Polymerization of hydrocarbon gases



' July 16, 1940 T. A. MANGELsDoRF Er A. `2,208,100

POLYMERIZATION OF HYDROCARBON GASES Filed D60. 8, 1955 FRACTIONATORS THEODORE A. MANGELSDORF Du Bols EASTMAN l INVENTOR ATTORNEY Patented July 16, 1940 UNITED STATES PATENT OFFICE POLYMERIZATION F HYDROCARBON GASES Theodore A, `Mangelsdorf and du Bois Eastman, Port Arthur, Tex., asslgnors to The Texas Company, New York, N. Y., a corporation of Delaware Application December 8, 1936, Serial No. 114,758

1 Claim.

15 jection of this latter gaseous fraction to catalytic l polymerization to form a polymer product containing lower boiling ends of gasoline in sufficient amount to meet the requirements in said lower boiling ends of gasoline of both polymer 20 products. In the thermal polymerization of hydrocarbon gases, there are formed in addition to a normally liquid hydrocarbon polymer, a gaseous fraction containing unreacted hydrocarbons and gaseous 25 reaction products containing a substantial amount of olefins. In the normal operation of a thermal polymerization process, usually the hydrocarbon gases containing from 2 to4 carbon atoms are recycled to the polymerization system.

30 Itis often undesirable to recycle a portion of these gases, particularly those of 4 carbon atoms containing butane and butenes, because the saturated C4 hydrocarbons are desirable for use as the lower boiling ends of gasoline to produce the 35 desired volatility of the finished product, and also the unsaturated vC4 hydrocarbons degrade under the influence of high temperature of the thermal polymerization operation. It is an object of the present invention to provide a more advantageous method for the utilization of a portion of the residual gases of the polymerization operation, particularly the butanes and butenes.

In accordance with the present invention, a hydrocarbon fraction, preferably one predominating in C4 hydrocarbons,4 is separated from the reaction products of a thermal polymerization process and this fraction processed separately in a catalytic polymerization operation. 'In the catalytic polymerization operation the unsaturated 50 hydrocarbons, such as the butylenes, are subjected to catalytic polymerization whereby larger yields of liquid polymer are obtained than would be produced by thermal polymerization, and a polymer product separated from the catalytic 55 polymerization operation containing normally liquid hydrocarbons resulting from the polymerization of the oleflns in addition to the residual saturated C4 hydrocarbons. It is a further object of the invention that the polymer from the catalytic polymerization operation contain volatile hydrocarbons or lighter ends ofgasoline, such as butane, in sumcient amount to meet the requirements in these light-ends of both the thermal and catalytic polymer, whereby these two polymer products may be blended to form a naphtha containing an amount of lower boiling or more volatile hydrocarbons, such as butane, suitable for the manufacture of commercial motor fuel.

More particularly, according to the process of the invention, normally gaseous hydrocarbons are subjected to polymerizing conditions of temperature and pressure whereby a substantial amount of normally liquid hydrocarbons is formed. A liquid hydrocarbon polymer is separated from the reaction products.- and it'is preferable that this l polymer be substantially free from hydrocarbons containing less than 5 carbon atoms. The remaining reaction products, after the separation of the liquid polymer, are fractionated to separate a fraction suitable for catalytic polymerization. Such fraction is preferably one predominating in Lhydrocarbons of 4 carbon atoms, although a 1 and `4 carbon atoms as well as a portion of the C4 hydrocarbons not used for the catalytic polymerization operation. The residual'gas, consisting chieiiy of methane and hydrogen, is released from the system.

The C4 fraction subjected to catalytic polymerization, consists essentially of a mixture of saturated and unsaturated hydrocarbons, such as butane and butenes. The unsaturated hydrocarbons are intended to be polymerized to normally liquid hydrocarbons while the saturated C4 hydrocarbons will pass through the system unchanged; It is difficult to make a separation between C4 hydrocarbons; consequently no attempt is ordinarily made to regulate by fractionation the proportions of saturated and unsaturated components of the C4 fraction from the thermal polymerization reaction products. Consequently.

these proportions will depend mainly on the conditions maintained in the thermal polymerization operation. Since the catalytic polymer will necessarily contain substantial amounts oi saturated C4 hydrocarbons, depending on the proportion of these constituents in the feed stock charged to the catalytic polymerization operation, the resultant catalytic polymer will ordinarily contain an excess of more volatile constituents, or saturated C4 hydrocarbons, such as butane. The catalytic polymer, therefore, is ordinarily used as blending stock and it is desirable that this 'blending stock be blended with a product decient in lighter ends of gasoline which may be supplied by the C4 hydrocarbons oi the catalytic polymer blending agent.

According to one method of operation, it is intended that the catalytic polymer be blended with the polymer produced in the thermal polymei-ization step. In this way the light constituents in the catalytic polymer will supply the requirements of low boiling constituents for the thermal polymer. In such an operation, in order to maintain the light constituents in the catalytic polymer in the right proportion to meet the requiremens of both the catalytic and thermal polymer when the two are blended, the amount of C4 fraction, derived from the thermal polymerization reaction and which is charged to the catalytic polymerization operation, may be regulated to insure the correct amount of residual C4 saturated hydrocarbons in the catalytic polymer.

The invention will be more fully understood from the following description, read in connection with the accompanying drawing, which shows diagrammatically an elevation of one form of apparatus for carrying out the process of the invention.

Referring to the drawing, hydrocarbon gas, such as natural or refinery gases or a fraction thereof, preferably a fraction predominating in butane or butane and propane, is subjected to polymerizing conditions of temperature and pressure in a heating coil I., located in a furnace 2. In this coil, the gases are raised to a conversion temperature which may range between 900-l100.

F., preferably about l0001050 F. under a pressure between 50G-5,000 kpounds and preferably around "15o-150D pounds, for suilicient time, which may range between 1-3 minutes, and preferably around one minute to one minute and a haii', whereby a substantial amount of normally liquid hydrocarbons essentially aliphatic in character is i'ormed. While only. a heating coil is shown, it is contemplated that a coil and reaction drum may be used. The reaction products are conducted from the heating coil I, through the line 3 to a heat exchanger 5 wherein the hot products of reaction pass in indirect heat exchange with the charge gases introduced into the heating coil I. In this heat exchanger, the temperature of the hot reaction products is reduced to about 450750 F. and preferably around' bottom of the fractionator through the line I4 controlled by the valve I5. This polymer is suitable for the manufacture of gasoline but is ordinarily decient in the more volatile yconstituents or light ends commonly occurring in commercial gasoline. 'I'he fractionation in the tower I2 is intended to be conducted so that the polymer contains substantially no hydrocarbons of a less number of carbon atoms than 5 or, in other words, substantially free from C4 hydrocarbons, such as butane and butenes and lighter materials. The gaseous reaction products substantially free from the normally liquid hydrocarbons are withdrawn from the top of fractionator I2 and conducted through the line I6 to a fractionator I 8. In the latter fractionator it is intended to separate a gaseous hydrocarbon fraction containing unsaturated hydrocarbons or oleiins suitable for polymerization in a catalytic polymerization operation. Such a fraction may comprise Ca and C4 hydrocarbons and preferably saturated and unsaturated C4 hydrocarbons such as butane and butenes. This hydrocarbon fraction is withdrawn from the bottom of the fractonator Il through the line 20 controlled by valve 2|, for further treatment, as will be described hereinafter. The remaining gaseous hydrocarbons, after the separation of a fraction suitable for catalytic polymerization, are conducted from the top of fractionator I8 through the line 22 and introduced into fractionator 25. In the latter fractionator a gaseous hydrocarbon fraction suitable for recycling to the system, is separated from residual gases, such as hydrogen and methane, which are released from the top of the fractionator 25 through the valve controlled line 26. The recycle stock separated in the i'ractionator 25, ordinarily comprises C3 hydrocarbons, and a portion or all of the C2 hydrocarbons, as well as a minor proportion of C4 hydrocarbons, depending on how eiilciently the C4 hydrocarbons are fractionated out in the fractionator I8. This recycle stock is withdrawn from the bottom of the fractionator 25 through the line 28, controlled by valve 30, by means of a pump 3|. 'Ihis recycle stock is combined with a fresh charging stock withdrawn` from a suitable source of supply, not shown, through the line 32 by the pump 34. The mixture of recycle stock and fresh charge is forced through the line 35 to heat exchanger 5 wherein it passes in indirect heat exchange with the hot products of reaction, as mentioned heretofore. In the heat exchanger the charging stock and recycle stock are preheated to a temperature of 200-600 F. and usually around 40G-500 F. The preheated mixture is then conducted through the line 36 to the heating coil I :wherein it is subjected to thermal polymerization.

Referring again to the hydrocarbon fraction Withdrawn from the bottom of the fractionator I8, for the purpose of catalytic polymerization, all or a portion of this fraction may be subjected to catalytic polymerization and the remainder, if any, recycled to the thermal polymerization. The portion of the fraction intended for recycling may be introduced into the recycle line 28 by suitable regulation of the valve 40 in the line 20. The gases intended for catalytic polymerization are withdrawn through the branch line 4I controlled by valve 42 and forced by pump 43 through the line 44 to a heating coil 45 located in a furnace 46. In the heating lcoil 45 the gases are heated to a temperature suitable for polymerization when contacted with a suitable catalyst. This temperature will range between 400-600" F.,

preferably around 45o-500 F. The hot gases are conducted through the line 48 to a series of catalyst chambers 49 and 50, connected by the line 5I. While two catalyst chambers are shown, any number may be used, connected in series or parallel, whereby they may be used continuously or intermittently. The catalyst chambers are provided with a suitable catalyst. such as aluminum chloride, sulfuric acid, phosphoric acid, etc. It is preferable to use phosphoric acid, supported on a suitable carrier such as silica gel, bauxite, etc. The gases are intimately contacted with the catalyst and the oleilns polymerized to normally liquid hydrocarbons. The reaction products are conducted through the line 52 to a fractlonator 5I wherein the desired polymer product is separated from any undesirable gaseous products which are withdrawn from the top of fractionator 5l through the line 56, controlled by the valve 51. These products removed from the top of the tower may consist of C3 hydrocarbons which have been incompletely separated from the charging stock in the polymerization operation and excess C4 hydrocarbons which may be undesirable for retention in the liquid polymer. These gases are ordinarily not great in volume and are conducted through the line 5B which communicates with the recycle line 28 whereby they may be recycled in conjunction with the recycle stock from the thermal polymerization operation to the thermal polymerizlng step. The polymer product separated in the fractionator 55 is withdrawn from the bottom of this fractionator through the line 60 and conducted to a rundown tank 6| which is provided with a valved draw-off line 62.

The polymer product from the catalytic polymerizatlon operation, 6|, contains saturated C4 hydrocarbons, such as butanes, which were unaffected by the catalyst in the catalytic polymerization operation. Ordi narily the amount of these C4 saturated hydrocarbons is considerably in excess of that required to render the catalytic polymer product suitable for motor fuel manufacture. This is intentional and advantageous because it is diflicult to separate saturated from unsaturated hydrocarbons of the same number of carbon atoms and accordingly the charging stock to the catalytic polymerizatlon, which ordinarily consists essentially of C4 hydrocarbons. will contain both saturated and unsaturated C4 hydrocarbons, the proportions of which will depend on the nature of the reaction products from the thermal polymerization operation. portion as possible of the C4 fraction separated from the reaction products of the thermal polymerization operation to the catalytic polymerization operation. It is desirable therefore, if possible, to charge all the C4 fraction removed from the fractionator I8 to the polymerization operation, and the amount of this material charged to the catalytic polymerization operation will ordinarily be limited only by the amount of the saturated C4 hydrocarbons which it is desirable to pass through the catalytic polymerization step. According to the present invention, it is intended that suflicient of this C4 fraction be charged to the catalytic polymerization operation to form a catalytic polymer product which will contain saturated C4 hydrocarbons in suiiicient amount to meet the requirement of low volatility constituents of both the thermal and catalytic polymer. Accordingly the catalytic polymer collected in the tank 6i should contain light constituents suchi as accumulated in the tank It is intended to charge as large a l butane in sufficient amount to satisfy the thermal polymer when blended therewith the thermal polymer may be conducted through the line il to the run-down tank Il and mixed with the catalytic polymer to` form a blend containing the correct proportion of light constituents for the manufacture of motor fuel. Ordinarily the amount of iight constituents such as butano in the blend will correspond to that which is ordinarily present in commercial gasolines.

The catalytic polymerization operation need not necessarily be dependent for a source of charging stock, entirely upon the fraction separated from the thermal polymerization operation. In case the catalytic unit has capacity sufiicient to treat extraneous gases or is a catalytic unit ordinarily operating on another charging stock, such as cracked or reiinery gases, which may be introduced through the charge line 6l, controlled by valve 6B, by means of a pump 01. this charging stock may constitute a minor or major proportion of the total feed for the catalytic unit. However, the effect and purpose of the charging stock derived from the thermal polymerization unit will not be defeated and the benefits obtained by the use of this charging stock, according to the present invention, may `still be realized.

As an example of the operation of the invention, a gaseous charging stock, consisting of about 70% butane and 80% propane, was subjected to thermal polymerization at a temperature of about 1030" F. under a pressure of approximately 2000 pounds with a reaction time of about seconds. The reaction products are conducted through a transfer line heat exchanger where they pass4 in indirect heat exchange with the fresh charge and recycle stock and thereby reduced in temperature to about '700 F. The partially cooled products are introduced into a' separator wherein higher boiling constituents, such as tars, etc., are separated, and the remaining reaction products subjected to fractionation to separate a liquid polymer and gase- .ous cuts consisting largely of C4 and C: hydrocarlmons respectively. The C: cut is recycled to the system and the C4 out subjected to catalytic polymerization under a pressure of about pounds at a temperature of about 500 F. in the presence of a phosphoric acid catalyst. The catalytic polymer product is separated and the thermal polymer is then blended with the catalytic polymer, the ratio ofthe volumes of the two being about 3:1 and to form a final product containing approximately the correct amount of light constituents, such as butane, for motor fuel pllIpOSeS.

The present invention has the advantage of avoiding the return of residual saturated C4 hydrocarbons to the thermal unit thereby eliminating considerable pumping and the recycling of excess products through the system. Furthermore, the recycling of the unsaturated C4 hydrocarbons which will be degraded in the thermal polymerization operation, is' largely eliminated. At the same time a catalytic polymer product is obtained in which the saturated Cr hydrocarbons are recovered and a resulting catalytic polymer product obtained which is desirable for blending with another naphtha deficient in high boiling hydrocarbons, such as the thermal polymer. The present invention may also advantageously be operated in connection with a catalytic polymerization operation inV which an extraneous unsaturated hydrocarbon gas, such as refinery g5 gases, is being processed,-and the butane content of the total catalytic product regulated, as desired.

Obviously many modications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof. and therefore only such limitations should be imposed as are indicated in the appended claim. Y

We claim:

A process for the manufacture of normally liquid gasoline hydrocarbons from normally gaseous hydrocarbons which comprises subjecting a normally gaseous fraction predominating in hydrocarbonsof between two and flve carbon atoms to polymerizing conditions of temperature of about 900 to 1100 F., and pressure of Vabout 500 to 5000 pounds, whereby normally liquid hydrocarbons are formed, separating from the reacgof'tion products a primary normally liquid polymer substantially free from hydrocarbons of less'than flve carbon atoms, also separating from the reaction productsa heavy gaseous fraction predominating in butane and butenes and a light 'gaseous traction predominating in hydrocarbons ondary polymer sumcient butane to meet the volatility requirements of both Athe polymers, recycling the excess butane to the thermal polymerization operation, and blending the polymers.

THEODORE A. MANGELSDRF. DUBOIS EASTMAN. 

